This invention relates to the handling of bulk materials and particularly to the unloading of bulk materials, such as coal, from the storage hopper or hoppers of a vessel.
The prior art has provided a variety of types of self-unloading cargo vessels for carrying bulk materials such as coal, ore, sand and gravel etc. These vessels are usually designed with the hull of the vessel being partitioned by bulkheads into a number of cargo holds, the latter being essentially large storage hoppers, the lower portions of which are generally of V-shaped cross-section, such hoppers usually extending substantially the full length of the vessel. A series of hopper gates are located at the bottoms of these storage hoppers, which gates open over one or more unloading belt-type conveyors which serve to convey the bulk material to additional equipment which transfers the bulk material to a location outside the vessel.
A serious problem with certain types of bulk materials, especially Western Canadian coal, is that they often tend to "bridge" over the openings of the conventional hopper discharge gates i.e. there is a tendency for the bulk material to "hang up" and form itself into a self-supporting arch over the hopper gate openings thus preventing the material stored above the arch from being discharged. Alternatively, the material can form a vertical wall both transversely and longitudinally of the hopper i.e. the material may fall, by gravity, over the gate and to one side of the hopper, leaving a longitudinal face on the other side which must be undermined in order to make it cascade into the hopper.
One rather primitive way of dealing with the above noted problem is to send one or more men into the hopper with picks and shovels in order that they can manually break up the "bridge" and allow the material to fall by gravity onto the moving conveyor. However, this approach is unsatisfactory in that there is a serious danger of the bridge or arch of material suddenly collapsing and carrying the men who are working on it down into the discharge opening. Thus, this approach involves a substantial degree of risk and personnel have been badly injured and in some cases killed, as a result of having used this particular approach.
In an effort to eliminate the above noted problem, various devices have been provided by the prior art as shown for example in Canadian Pat. No. 564,070 issued Sept. 30, 1958 to Borrowdale, Canadian Pat. No. 857,706 issued Dec. 8, 1970 to Martini et al and U.S. Pat. No. 3,604,578 issued Sept. 14, 1971 to Smith. The first one of the above noted patents incorporates apparatus which may travel beneath the hopper and extend upwardly into the material in the hopper through the hopper bottom, the device being rotated in an effort to agitate the material in the hopper so as to break up any adhering or cohering condition which may exist thereby inducing the material to flow by gravity from the hopper. The second patent noted above includes a feeder which includes two rotary plow mechanisms for reclaiming bulk material from two inclined storage shelves located at the bottom of the vessel storage area. The last patent noted above incorporates inflatable means on the sloping hopper walls which means can be inflated and deflated thereby to loosen the bulk commodity thus reducing the tendency for "bridges" to form over the discharge opening.
The above noted patents are exemplary only of the various arrangements provided by the prior art. These and other prior art devices do not appear to have found wide acceptance, at least in vessels being operated on the Great Lakes of North America, possibly because they were not found to be as effective as intended and/or because they required costly modifications to the vessel structure or alternatively, different designs of hopper arrangements for the vessels were required.